Carter, R.M., McCave, I.N., Richter, C., Carter, L., et al., 1999 Proceedings of the Ocean Drilling Program, Initial Reports Volume 181 6. SITE 1122: TURBIDITES WITH A CONTOURITE FOUNDATION1 F1. Locality map for Site 1122, Shipboard Scientific Party2 p. 38. ° CS - Cook Strait 25 S FS - Foveaux Strait HT - Hikurangi Trough MS - Mernoo Saddle D = Dunedin T = Timaru C = Christchurch Louisville Seamount chain K = Kaikoura 30° W = Wellington N = Napier G = Gisborne Kermadec Trench 35° North Island G 1124 N HT 40° 284, 593 CS W 1125 1123 K C MS Chatham Rise Chatham Is. T South 45° Island Bounty D 1119594 Trough 2023 FS 30341122 Stewart Is. BACKGROUND AND OBJECTIVES Bounty Is. 1120 Bollons 275 ° Auckland Is. Seamount 50 276 279 Campbell Plateau 1121 Solander 277 Trough Campbell Is. 200 General Description 500 1000 ODP 55° 2000 3000 4000 Leg 181 278 Site 1122 is located 275 km south of the Chatham Islands, midway 5000 between the Chatham and Bounty Islands, and 830 km east of Dune- 160°E 165° 170° 175° 180° 175°W 170° din, eastern South Island (Fig. F1). The site was drilled in a water depth of 4432 m on the left (north) bank levee of the abyssal Bounty Fan. The F2. Portion of seismic lines, p. 39. fan is located in the most seaward axial deep of the Bounty Trough, a A Cretaceous rift basin formed during the separation of New Zealand and Southwest 10km Site 1122 6 Bounty Antarctica across the newly forming mid-Pacific Rise (Carter and Carter, Channel 1993, 1996; Davey, 1993). The Bounty Channel feeds sediment along R3 A R5 R7 B C the axis of the trough and onto the adjacent 95-Ma oceanic crust of the R9 Southwest Pacific abyssal plain. Two-way traveltime (s) D1 7 R10 Site 1122 is located on New Zealand Oceanographic Institute (now D2 R11 NIWA) single-channel seismic and 3.5-kHz line 88-2023 (Figs. F2A, F2B, NZOI 2023 Basement F3). The three main units that compose the Bounty Fan at this crossing (seismic Units C–A; Table T1) all show strong angular onlap onto the folded surface of pre-Unit C sediments. In ascending order, and at the F3. Portion of 3.5-kH line, p. 41. drill site (Fig. F2B), these units consist of 150 ms of irregularly and 2km Northeast lightly reflective sediment (Unit C, capped by a strong reflector, R-7), 75m Channel margin 110 ms of thin-bedded and regularly reflective sediment passing up into Site 1122 strongly reflective sediment (Unit B, capped by reflector R-5), and upper Unit A which is 470 ms thick and comprises a field of spectacular sedi- NZOI 2023 ment waves. The waves initiate as small features just above reflector R5, 1 (the Unit B/A boundary), and grow in both wavelength (up to 6 km Examples of how to reference the whole or part of this volume. apparent) and height (up to 17 m) as they rise through the sediment 2Shipboard Scientific Party pile to the seabed, where they were apparently still active in the recent addresses. past (Carter et al., 1990). The sediment waves are best developed, and Ms 181IR-106 SHIPBOARD SCIENTIFIC PARTY CHAPTER 6, SITE 1122: TURBIDITES WITH A CONTOURITE FOUNDATION 2 were drilled, beneath the 315-m-high north bank levee of the Bounty Channel. Similar waves, though of smaller amplitude, occur under- neath the 90-m lower crest of the south bank of the Bounty Channel. Sediment waves have been described from a number of Northern Hemi- sphere deep-sea environments, including submarine fans where they are most prominent on channel right banks (Damuth, 1979; Normark et al., 1980; Brew, 1995). Fan levees are inferred to have been built by overspilling turbidity currents, whose top surfaces are deflected right or left, according to the effect of Coriolis force on fluids in motion in the Northern and Southern Hemispheres, respectively (Menard, 1955; Komar, 1969). As a turbidity current overtops its levee, it may develop a series of antidune surges that cause the formation and growth of sedi- ment waves across the levee crest (Normark et al., 1980). The sediment waves form the upper unit (A) of the fourfold seismic stratigraphy we describe (Table T1). A zone of harder acoustic reflection T1. Summary of seismic unit extends down from the floor of the present-day channel obliquely to depth and reflectors, p. 83. the left (south), where it has its initiation at or a little above reflector R9 (Fig. F2A). This zone marks the movement through time of the axis of the paleo-Bounty Channel. Seismic Units C–A compose the core of the Bounty Fan, and all appear to have been deposited as part of the north bank levee of the Bounty Fan’s main sediment feeder, the Bounty Chan- nel. The fan sediments rest on a regional unconformity (Y), here equiv- alent to reflector R9, below which the sediments of Unit D are gently folded and eroded. The lateral equivalents of Unit D are exposed in the inner and outer sills of the Bounty Trough, where dredged samples have provided Miocene microfossils, suggesting that the deformation and unconformity formation were of middle late Miocene age. The lower part of Unit A has been dated previously as late Pliocene (Mangapa- nian), on the basis of a microfauna cored from the lower north wall of the channel (Carter et al., 1994). Site Objectives Site 1122 was drilled to establish the history of deposition of the Bounty Fan, and the degree to which fan-growth has been affected by the fact that the current fan is building out into the path of the South- west Pacific Deep Western Boundary Current (DWBC). For instance, a breach in the left bank levee of the fan, at depths of ~4650 m, may have been caused by DWBC erosion or may be a turbidity current avulsion point maintained by the boundary flow. The current may also be caus- ing sediment unmixing and sand mobility across the middle and lower fan (Carter and Carter, 1996). The sediment waves under the left bank levee are the subject of an earlier study by Carter et al. (1990), who described core and 3.5-kHz profile evidence for the presence of alternat- ing cycles of glacial turbidite deposition and interglacial biopelagic ooze accumulation. Carter and Carter (1992) therefore interpreted the pat- tern of regular reflectors on deep seismic profile NZ01 2023 as evidence for a similar glacial/interglacial pattern of lithologic change with depth, and, by comparison with the global isotope stage record, predicted an isotope Stage 100 (~2.4 Ma) age for reflector R7 of this study (Table T1). The Site 1122 cores were expected to yield a test of this prediction. Finally, because of the location of the site just south of the Subtropical Convergence (STC), information from Site 1122 should help test for the stability of position of the STC between glacial and interglacial times (Fenner et al., 1992; Nelson et al., 1993; Weaver et al., 1998). SHIPBOARD SCIENTIFIC PARTY CHAPTER 6, SITE 1122: TURBIDITES WITH A CONTOURITE FOUNDATION 3 OPERATIONS Hole 1122A The 341-nmi voyage to Site 1122 (proposed site SWPAC-8A) was accomplished at an average speed of 9.6 kt. The vessel proceeded directly to the Global Positioning System coordinates of the location. The positioning beacon was dropped at 2254 hr on 5 September. The hydrophones and thrusters were extended and the vessel settled on location. The advanced hydraulic piston core/extended core barrel 7 (APC/XCB) bottom-hole assembly (BHA) was assembled using a 9-⁄8 -in PDC bit. Hole 1122A was spudded with the APC at 1210 hr on 6 Sep- tember. The recovery indicated that the water depth was 4435.00 meters below sea level (mbsl). Piston coring advanced to refusal at 75.8 mbsf, and Cores 1H through 8H were taken (Table T2, also in ASCII for- T2. Site 1122 expanded coring mat). The hole was deepened with the XCB to 123.9 mbsf, which was summary, p. 84. considered the objective for the initial hole of the site. APC cores were oriented starting with Core 181-1122A-3H. The bit cleared the seafloor at 0415 hr on 7 September, ending operations at Hole 1122A. Hole 1122B The vessel was offset 20 m to the west and the second hole of the site was spudded with the APC at 0615 hr on 7 September. To obtain a stratigraphic overlap for interhole correlation, the bit was positioned 5 m higher than at Hole 1122A. However, the recovered core barrel was full, which required another attempt to obtain a mudline core. Hole 1122C The bit was raised at the same location by an additional 5 m, and Hole 1122C was spudded with the APC at 0740 hr. The mudline core indicated that the water depth was 4431.80 mbsl. The APC was advanced by recovery to 103.7 mbsf and Cores 1H through 13H were obtained (Table T2). The last three cores (11H, 12H, and 13H) did not achieve a full stroke. Coring was switched to the XCB and advanced without incident to 204.3 mbsf with good to poor recovery (Table T2). Very rapid XCB cor- ing continued with recovery ranging from 1% to 97% from 204.3 to 627.4 mbsf. After making a drill pipe connection following the retrieval of Core 68X (617.8 to 627.4 mbsf), the drill string became stuck and could not be rotated with up to 700 A of top drive current. The driller worked the pipe for over an hour with overpulls as large as 200 kilopounds (kips), while maintaining a circulation rate of 1000 gal/min at 2200 psi pressure before the drill string came free.